1. Field of the Invention
This invention relates to a method and an apparatus of treating positive photoresist materials applied on semiconductor wafer and, more particularly, to a method and an apparatus of treating the developed positive photoresist image on a semiconductor wafer placed in a chamber by employing ultraviolet irradiation.
2. Description of the Prior Art
As for the prior-art treatment of positive photoresist employing ultraviolet irradiation, exposing the photoresist to ultraviolet radiation is utilized in a treatment in which the same pattern as a mask pattern is formed on the photoresist film applied on a semiconductor wafer, etc., and recently attention has been paid to the application of this method to particular treatments such as the treatment of baking said photoresist film on a wafer.
The baking process is employed between a process of "forming a photoresist pattern, exposing and developing the photoresist" and a process of "executing ion implantation, plasma-etching, etc.", and said process is composed of a heating process executed for improving the adhesiveness of the photoresist to a semiconductor wafer and heat-resistance of said photoresist. While a reference of H. Hiraoka and J. Pacansky: J. Vac. Sci. Tech. 19(1981), and U.S. patent application Ser. No. 923,553 have disclosed a method in which ultraviolet rays are applied to the developed positive photoresist image after or during the baking process after "development process" so as to enhance the heat-resistance and plasma-resistance of the positive photoresist thorough the baking process in a shorter time.
When a light having a high ultraviolet intensity, such as a radiant light from a discharge lamp such as high pressure mercury vapor lamp having a high ultraviolet radiation efficiency, is applied to the developed positive photoresist film to expedite the treatment, however, gas is generated from the photoresist, and this gas causes the formation of bubbles, deformation of a photoresist pattern and breakdown of a photoresist film, such as exfoliation, rupture or roughening hereof, thus causing imperfections of a semiconductor device.
It can be supposed that the generation of this gas is caused by a rapid photochemical reaction of the light sensitive radicals of the photoresist materials, for instance, by the photochemical reaction of HMDS(hexamethyldisilazine), which is applied to a wafer as a preliminary treatment for the good coating of the photoresist onto a wafer or of an anti-reflection coating on the photoresist film, by the photochemical reaction of an additive materials to the photoresist materials such as dyestuff, by the photochemical reaction of a solvent remaining in the photoresist film.
These photochemical reactions are advanced remarkably by a light having a wavelength 300 nm to 500 nm, and more particularly, by a light having a wavelength in the spectral response region of the photoresist materials. Accordingly, when a discharge lamp such as a high pressure mercury vapor lamp radiating a light including these wavelength region is employed, it is not always to enhance the radiation light in order to shorten the time of treating the developed positive photoresist on a wafer. In other words, this apparatus has a problem that it cannot perform a high-speed treatment.